Chiral phosphine ligands have been widely used as components of transition metal catalyts, which catalysts are useful for carrying out asymmetric synthesis. Although many methods for making chiral phosphines are known, the chiralities of most of these ligands rely mainly on a chiral substituent group to impart chirality to the resulting phosphine ligand. In contrast, only a limited number of P-chiral ligands have been prepared, presumably because no general and efficient methods are available for their synthesis.
In the 1970s Knowles and coworkers prepared the first prominent P-chiral ligand DIPAMP (see, e.g., reviews by Methot, J. L. et al. Adv. Synth. Catal. 2004, 346, 1035-1050; Seayad, J. et al., Org. Biomol. Chem. 2005, 3, 719-724; Connon, S. J. Angew. Chem., Int. Ed. 2006, 45, 3909-3912; and Benaglia, M. et al. Org. Biomol. Chem. 2010, 8, 3824-3830). However, methods for the synthesis of optically active P-chiral phosphines have emerged slowly. Representative methods include the formation and separation of diastereomeric mixtures of menthyl phosphinates, auxiliary-based transformations, enantioselective deprotonation of phosphine-boranes and sulfides, enzymatic resolution, transition metal catalyzed asymmetric phosphine alkylations, dynamic kinetic asymmetric oxidation of racemic phosphines, and through H-menthylphosphinates. Despite these elegant approaches, the currently available methods are often limited in terms of substrate scope and practicality, especially for the synthesis of sterically crowded P-chiral phosphines.
Thus, there is a need to provide a general, practical, and high stereoselective method for the synthesis of P-chiral compounds with diverse structures and functionalities.